U.S. Pat. No. 6,271,319 describes a process for polypropylene manufacturing, including treating a vent stream from the polymerization reactor, to recover propylene for return to the reactor. The process involves using a gas separation membrane to separate propylene from propane in the reactor vent stream. The membrane separation step results in a residue stream typically containing as much as 30% propane or more, which is vented from the polymerization process, and a permeate stream containing 95% or less propylene, which is recirculated to the polymerization reactor. The membrane separation operates on a rich propylene stream.
WO 2005-082957 describes a process for making polypropylene. The process comprises contacting an oxygenate stream with an olefin forming catalyst to form an olefin stream. An intermediate grade propylene stream is separated from the olefin stream, with the intermediate grade propylene stream preferably containing less than 99.5 wt % propylene, based on total weight of the stream. In one embodiment, the intermediate grade propylene stream is contacted with a polypropylene forming catalyst to form polypropylene and unreacted by-product. Propane is removed from the unreacted by-product to form at least one purge stream and a propylene containing recycle stream. At [0092] is cited “In general, propane and propylene will be recovered by way of the purge stream and, preferably, a substantial portion of the propane is separated from the unreacted propylene so that a substantial amount of propane is not recycled to the reaction process. Such separation of propane from the purge stream can be accomplished by conventional means, including distillation or separation using molecular sieves or membranes.”
WO 2008-084415 relates to a process for the membrane-based separation of propane and propylene, said process comprising the steps of: feeding a feed stream comprising propylene and propane to a first membrane, said first membrane comprising a feed port, a residue port, and a non-permeate port, at a temperature at or slightly above the dewpoint of propylene and a pressure between about 400 psia and about 600 psia, said first membrane having a selectivity for propylene of at least 6.5, whereby at least a portion of a first non-permeate stream condenses on or about said first membrane; and extracting a first permeate propylene enriched stream, wherein said permeate stream is extracted at or about the same temperature as said feed stream. The propylene propane separation is cited but there is no link with a propylene polymerization zone.
US 2004-000513 discloses an apparatus for economical separation of fluid mixtures. Broadly, apparatus of the invention comprises modules using solid perm-selective membranes. More particularly, the invention relates to a plurality of membrane modules disposed in a first product group, a second product group, and optionally one or more intermediate group. Apparatus of the invention with the membrane modules in multiple groups is beneficially useful for simultaneous recovery of a very pure permeate product and a desired non-permeate product from a mixture containing organic compounds. There is no link with a propylene polymerization zone.
US 2006-266213 relates to methods for treating a gas mixture of at least propylene and propane, in order to separate the propylene from the propane. The gas mixture is brought into contact with a membrane enabling the selective permeation of the propylene with respect to the propane. A propylene-enriched permeate and a propane-enriched retentate is formed. The propylene concentration of the permeate in the membrane is then reduced with a sweeping gas. This process is used in connection with a propylene polymerization zone but there is no propylene-propane splitter.
US 2004-182786 Apparatus and processes are disclosed for economical separation of fluid mixtures. Broadly, apparatus of the invention is an integrated fractional distillation and perm-selective membrane separation apparatus. More particularly, the integrated apparatus comprises a fractional distillation column and one or more membrane device utilizing solid permselective membranes. Processes of the invention are particularly useful for simultaneous recovery of a very pure permeate product, a desired non-permeate stream, and one or more distillate products from a fluid mixture containing at least two compounds of different boiling point temperatures. There is no link with a propylene polymerization zone and the membrane operates on a rich propylene stream.
FR 2886646 describes a process for separating one or more compound(s), including at least one n-paraffin, in a hydrocarbon feedstock, in which: A stream, or a portion of a stream of said feedstock, is passed successively and in any order into at least one distillation column and at least one membrane separation unit comprising a selective membrane with regard to at least one n-paraffin; and one or more stream(s) is (are) recovered from the column and the membrane separation unit, each of said streams being enriched respectively with one of said compounds, and at least one of said streams being enriched with at least one n-paraffin. Installation for the implementation of this process. The invention relates in particular to a process and an installation that allow the fractionation of a petroleum fraction that contains hydrocarbon molecules with close boiling points. There is no link with a propylene polymerization zone.
WO 2009-106706 describes a propane/propylene separation process employing a distillation column and at least one membrane separation unit consisting of one or more modules working in series, said membrane separation unit being placed either upstream, or downstream, or upstream and downstream of the distillation column. There is no link with a propylene polymerization zone.
It has now been discovered a new process for the purging of propane in a polypropylene manufacturing process